The present invention concerns the field of cars, and in particular that of the circulation of air for cooling the engine equipment.
Vehicles that have a heat engine need to discharge the calories that they generate during operation, and are equipped for this purpose with heat exchangers, in particular coolers, which are generally positioned at the front of the vehicle and through which outside air passes. A fan is positioned upstream or downstream in order to force this air to circulate through the exchanger or exchangers. The ventilation blower wheel that forces the air to circulate has a flow oriented in an axial direction. It comprises blades that are connected by the root to a central hub, and generally held together at the tip by a rotating guide (as shown in FIG. 1).
It is also usual to give the blades curvature effects in order to improve their acoustics. The curvature is referred to as forward curvature if the blade is curved in the direction of rotation, considered according to the plane perpendicular to the axis of rotation; otherwise, it is referred to as backward curvature. Using the curvature effects, the acoustic sources that are located along the span of the blade are phase-shifted from each other, and tonal noise reductions of several decibels can be observed.
In addition to having beneficial acoustic effects, curvature also modifies the aerodynamic properties, because it produces forces perpendicular to the blade surface, said forces in turn creating radial flows. Generally, for a given operating point, backward curvature will produce a flow extending radially outwards, while forward curvature has the effect of contracting the flow (as will be explained in greater detail in relation to FIG. 2). Therefore, backward curvature works more at the tip, and promotes efficiency at high flow rates, while forward curvature promotes low flow rates, working more at the root.
However, from an aeroacoustic point of view, the advantages are reversed and backward curvature produces more noise at a high flow rate owing to the greater amount of work at the tip, while forward curvature produces more noise at a low flow rate owing to the greater amount of work at the root. It is therefore observed that the benefits of a (forward or backward) curvature effect are antagonistic and that, owing to this effect, it is not possible to achieve both satisfactory aerodynamic efficiency and satisfactory acoustic quality in a same operating range (low or high flow rate).
Mixed solutions incorporating backward curvature and forward curvature are therefore an often-used compromise. These mixed backward/forward curvatures have the effect of contracting the flow, which centers approximately at the mid-span point (see FIG. 2). However, owing to these particular mid-span flow conditions, the pressure gradient between the trailing edge and the leading edge is modified, and significant separation is observed on the suction face of the blade, originating in this mid-span area.
There is therefore a need to design improved blower wheels that are capable of producing high aerodynamic efficiency without suffering a drop in aeroacoustic performance.